The present invention relates to technique for pretreatment such as degreasing or chemical treatment to surfaces of work or metallic surfaces soiled with rust preventing oil, oil used for press forming, cutting oil, or machining oil.
Zink phosphating is widely used for metallic material such as steel or galvanized metal in order to improve the rust preventive characteristic and the paint adhesion. In general, the process of zinc phosphating includes a sequence of degreasing, rinsing, surface conditioning, chemical treatment (or zinc phosphating), rinsing, and drying. Degreasing operation, rinsing operation and surface conditioning operation may be performed a plurality of times, according to the need.
For a zinc phosphate chemical conversion coating to achieve, as a substrate layer for painting, sufficient effects of rust prevention and paint adhesion, it is desirable to obtain a uniform, fine crystalline coating having a coating weight in the range of 2˜5 g/m2. To obtain such a coating layer, one process employs a degreasing operation, and a surface condition operation with a titan colloid type treatment liquid.